1. Field of the Invention
The present invention relates to a method and apparatus for handling and drying sheets which contain wet ink jet images. More specifically, the invention relates to an apparatus for passively drying printed sheets and sequentially stacking the dried printed sheets.
2. Description of the Related Art
Ink jet printing demands that excess moisture (generally water) on the surface of printed sheets be removed within a set time period and before the sheets are stacked. If the sheets are stacked before the images are dry, image smearing and offset occur.
Devices that actively remove moisture, specifically water, from the sheet surface are referred to as dryers. A commonly used dryer is a hot air convective mass transfer drying system. While dryers are effective in rapidly removing the excess moisture from the sheets, dryers greatly increase printer power requirements and size. If dryers were used in small printers, the size and cost of these printers would greatly increase. Also, most small printers do not have the power capacity to accommodate an active dyer.
U.S. Pat. No. 4,970,528 to Beaufort et al. discloses an ink jet printing apparatus having a uniform heat flux dryer system which uses an infrared bulb and reflectors to transmit heat to the printed paper during the ink drying process. The freshly printed sheet is dried as it is fed from the printing apparatus along a 180.degree. arc which surrounds the infrared bulb and reflectors.
U.S. Pat. No. 4,982,207 to Tunmore et al. discloses an ink jet printer having a rotary platen with a heater contained therein. The platen is made of a heat conducting material to transmit the heat from the heater unit enclosed therein to the outer surface of the platen to dry the printed sheet before it is fed to a stacking unit.
U.S. Pat. No. 2,306,607 to Horton discloses a web drying device for sheets printed by an intaglio printing apparatus. The web drying device feeds the web along a series of rollers while exposing the web to heat blown onto the web by an exhaust fan.
The prior art references all teach the use of some type of active heating element to dry the freshly printed sheets. As discussed above, these active dryers demand increased printer power capacity and also increase the size and cost of the printing apparatus which is unacceptable for a small, relatively inexpensive printer. Thus, these small printers must rely on passive drying systems to dry the wet sheets to maintain their low cost. However, most passive drying systems require large areas to avoid wet sheets from contacting any surface which will cause smearing and therefore, greatly increase the size of the printer.
None of these references provides a passive dryer for small printers which dries ink jet printed sheets while the sheets are fed from the printing apparatus to a stacking tray.